1. Field of the Invention
This invention relates to equipment for handling and placing optical fibers.
Optical fibers are used commonly for transmission of digital data because they are capable of transmitting high volumes of data due to their large bandwidth. The fibers and components to which the fibers must be connected for functionality are very small and therefore difficult to easily manipulate and work with. An optical fiber might be only 80 microns in diameter, and components such as transmitters, receivers and transducers might not be more than 100 microns in typical dimensions.
Given the precision required for handling and connecting optical fibers to components, use of robots in the process results in higher-quality end products and reduces the rejection rate of the assembled equipment. However, because of the small dimensions of an optical fiber, automation of the handling and positioning of the fiber has always posed considerable difficulty.
2. Description of the Prior Art
There are a number of types of devices currently available for handling optical fibers, three of which are discussed below.
The first type uses an upwardly-opening groove, into which the fiber is placed. A "lid" is then placed over the optical fiber to hold the fiber firmly between the lid and the groove. In the closed state, the lid must be mechanically locked into position.
The second type is similar in concept to the first type. A groove is provided in a simple cylinder. The optical fiber is pushed into the groove, so that the fiber sits below the outer circumference of the cylinder. A cover, such as a sheath, is placed over the cylinder to prevent the optical fiber from slipping out.
Both of the above types of devices apply mechanical pressure to the fiber in order to hold the fiber in place. The mechanical pressure however may damage the fiber and potentially change its optical characteristics. Also both types strongly depend on the diameter of the optical fiber in order to secure a hold on the fiber. Automating these grippers is difficult for a variety of reasons, including relative bulkiness, the need of a human operator to place the fiber into the gripper, the weight of the grippers, and the gripper size relative to the placement accuracy needed.
The third type of device involves soldering or welding a T-shaped or L-shaped "handle" to the fiber. A gripper can then pick, orient, and place the fiber by moving the handle. This requires applying heat to the end of the optical fiber to attach and detach the handle, increasing the risk of damage to the fiber. During the removal phase, the fiber may move, thereby reducing the quality of the finished product.
The invention uses a vacuum gripper, as will be described in greater detail later. Vacuum has been used previously by stationary grippers to hold an optical fiber steady, as disclosed in U.S. Pat. Nos. 5,135,590, 5,386,490, and 5,185,846, for example, but vacuum does not appear to have been used in a moveable gripper to grip, move and position an optical fiber.
Apart from the difficulty in handling optical fibers, determining the fiber's position with precision is also difficult. To properly connect the optical fiber to a component, accurate positioning and position determination are both essential, if reject rates are to be kept at acceptable levels. There is therefore a need for apparatus which can effectively grip the fiber, determine its position, and move it precisely to the desired position. One of the most common methods of determining position for automation purposes is to use a vision system to capture and analyze an image of the fiber by standard image processing software. However, because the fibers are largely transparent under normal direct illumination, they are more or less invisible to a camera, even with normal contrast enhancement. The image which may be obtained from them does not have sufficiently sharp defining lines to be used by the image processing software. There is therefore a need to provide sufficient contrast to enable the vision system to capture an image which permits the position of the fiber to be readily ascertained.